Ozone, which causes photochemical smog, is produced by a photochemical reaction of HC and NOx contained in exhaust gases from automobiles and factories. Therefore, reducing the amount of HC and NOx emissions from automobiles is an efficient way to suppress the production of ozone and prevent the occurrence of photochemical smog. Also, purifying ozone in the air directly can be one way to prevent the occurrence of photochemical smog. By purifying ozone as a product while reducing the amount of emissions of HC and NOx as reactants, the occurrence of photochemical smog can be prevented more effectively. Thus, an automobile including an air cleaner for a vehicle capable of directly purifying ozone in air has been put into practical use in some places including California in the United States of America. Such a cleaner is called a DOR (Direct Ozone Reduction) system.
For example, Patent Literature 1 discloses a DOR system in which a vehicle component such as a radiator carries a metal oxide such as manganese dioxide. The radiator is disposed at such a position as to be exposed to air during travel of a vehicle, and the manganese dioxide has a function of converting ozone contained in the air into other elements such as oxygen and purifying the ozone. Thus, according to the DOR system disclosed in Patent Literature 1, ozone in air can be directly purified while the vehicle travels is moving.